1. Field of the Invention
This invention relates to positioning of rigid sheet material, and in particular to accurate positioning of a glass sheet for numerical controlled cutting, edging, and/or drilling operations.
2a. Technical Considerations
Glass sheets are fabricated to various shapes to conform with the outlines required for fabricated products, such as automobile and aircraft windows and the like. To be suitable for such applications, flat glass sheets must be shaped to precisely defined curvatures dictated by the shape and outline of the frames defined in the window opening in the vehicle. Each glass shape is unique and has different peripheral configurations. As a result, in a conventional glass cutting and edging operation, the equipment must be shut down, repositioned and modified for each different glass part. In response to the need to reduce the amount of down-time during a change in the glass pattern, numerically controlled technology has been incorporated into the cutting and edging operation. This technique uses computer controls to coordinate the movement of the tools to cut and edge a glass part from a glass sheet, so that a change in glass pattern is effected by using a computer program that corresponds to the desired part. It is extremely important that the glass sheet be precisely positioned prior to any operation since the programming for the movement of the tool is based on a predetermined position of the glass sheet.
2b. Patents of Interest
U.S. Pat. No. 3,641,711 to Halberschmidt et al. teaches an apparatus for grinding the edge of a glass plate wherein the glass plate is lowered onto a support table and centered between a plurality of centering jaws.
U.S. Pat. No. 4,064,659 to Ulivi teaches an apparatus for centering sheets of glass on a machine platform, including pin carrying supports that move the pins from a rest position in which the pins are turned down below the plane of the glass sheet and retracted from the sheet to an upright working position in which the pin is advanced into engagement with the glass sheet.
U.S. Pat. Nos. 4,200,420 to Cathers et al., and 4,228,993 to Cathers teach a sheet orienting and transporting frames having a plurality of aligning devices to orient the glass relative to the frame before it is lifted and transported by the frame.
U.S. Pat. No. 4,347,927 to Landes teaches an apparatus for aligning and advancing a plastic and glass sheet assembly on a conveyer for proper entry into the receiving zone of a pressing apparatus.